Buggy code:
public class FileUtils { public FileUtils ( ) { } public static final long ONE_KB = 1024 ; public static final BigInteger ONE_KB_BI = BigInteger . valueOf ( FileUtils . ONE_KB ) ; public static final long ONE_MB = ( FileUtils . ONE_KB ) * ( FileUtils . ONE_KB ) ; public static final BigInteger ONE_MB_BI = FileUtils . ONE_KB_BI . multiply ( FileUtils . ONE_KB_BI ) ; private static final long FILE_COPY_BUFFER_SIZE = ( FileUtils . ONE_MB ) * 30 ; public static final long ONE_GB = ( FileUtils . ONE_KB ) * ( FileUtils . ONE_MB ) ; public static final BigInteger ONE_GB_BI = FileUtils . ONE_KB_BI . multiply ( FileUtils . ONE_MB_BI ) ; public static final long ONE_TB = ( FileUtils . ONE_KB ) * ( FileUtils . ONE_GB ) ; public static final BigInteger ONE_TB_BI = FileUtils . ONE_KB_BI . multiply ( FileUtils . ONE_GB_BI ) ; public static final long ONE_PB = ( FileUtils . ONE_KB ) * ( FileUtils . ONE_TB ) ; public static final BigInteger ONE_PB_BI = FileUtils . ONE_KB_BI . multiply ( FileUtils . ONE_TB_BI ) ; public static final long ONE_EB = ( FileUtils . ONE_KB ) * ( FileUtils . ONE_PB ) ; public static final BigInteger ONE_EB_BI = FileUtils . ONE_KB_BI . multiply ( FileUtils . ONE_PB_BI ) ; public static final BigInteger ONE_ZB = BigInteger . valueOf ( FileUtils . ONE_KB ) . multiply ( BigInteger . valueOf ( FileUtils . ONE_EB ) ) ; public static final BigInteger ONE_YB = FileUtils . ONE_KB_BI . multiply ( FileUtils . ONE_ZB ) ; public static final File [ ] EMPTY_FILE_ARRAY = new File [ 0 ] ; private static final Charset UTF8 = Charset . forName ( "UTF-8" ) ; public static File getFile ( File directory , String ... names ) { } public static File getFile ( String ... names ) { } public static String getTempDirectoryPath ( ) { } public static File getTempDirectory ( ) { } public static String getUserDirectoryPath ( ) { } public static File getUserDirectory ( ) { } public static FileInputStream openInputStream ( File file ) throws IOException { } public static FileOutputStream openOutputStream ( File file ) throws IOException { } public static FileOutputStream openOutputStream ( File file , boolean append ) throws IOException { } public static String byteCountToDisplaySize ( BigInteger size ) { } public static String byteCountToDisplaySize ( long size ) { } public static void touch ( File file ) throws IOException { } public static File [ ] convertFileCollectionToFileArray ( Collection < File > files ) { } private static void innerListFiles ( Collection < File > files , File directory , IOFileFilter filter , boolean includeSubDirectories ) { } public static Collection < File > listFiles ( File directory , IOFileFilter fileFilter , IOFileFilter dirFilter ) { } private static void validateListFilesParameters ( File directory , IOFileFilter fileFilter ) { if ( ! ( directory . isDirectory ( ) ) ) { <START_BUG> throw new IllegalArgumentException ( "Parameter<seq2seq4repair_space>'directory'<seq2seq4repair_space>is<seq2seq4repair_space>not<seq2seq4repair_space>a<seq2seq4repair_space>directory" ) ; <END_BUG> } if ( fileFilter == null ) { throw new NullPointerException ( "Parameter<seq2seq4repair_space>'fileFilter'<seq2seq4repair_space>is<seq2seq4repair_space>null" ) ; } } private static IOFileFilter setUpEffectiveFileFilter ( IOFileFilter fileFilter ) { } private static IOFileFilter setUpEffectiveDirFilter ( IOFileFilter dirFilter ) { } public static Collection < File > listFilesAndDirs ( File directory , IOFileFilter fileFilter , IOFileFilter dirFilter ) { } public static Iterator < File > iterateFiles ( File directory , IOFileFilter fileFilter , IOFileFilter dirFilter ) { } public static Iterator < File > iterateFilesAndDirs ( File directory , IOFileFilter fileFilter , IOFileFilter dirFilter ) { } private static String [ ] toSuffixes ( String [ ] extensions ) { } public static Collection < File > listFiles ( File directory , String [ ] extensions , boolean recursive ) { } public static Iterator < File > iterateFiles ( File directory , String [ ] extensions , boolean recursive ) { } public static boolean contentEquals ( File file1 , File file2 ) throws IOException { } public static boolean contentEqualsIgnoreEOL ( File file1 , File file2 , String charsetName ) throws IOException { } public static File toFile ( URL url ) { } static String decodeUrl ( String url ) { } public static File [ ] toFiles ( URL [ ] urls ) { } public static URL [ ] toURLs ( File [ ] files ) throws IOException { } public static void copyFileToDirectory ( File srcFile , File destDir ) throws IOException { } public static void copyFileToDirectory ( File srcFile , File destDir , boolean preserveFileDate ) throws IOException { } public static void copyFile ( File srcFile , File destFile ) throws IOException { } public static void copyFile ( File srcFile , File destFile , boolean preserveFileDate ) throws IOException { } public static long copyFile ( File input , OutputStream output ) throws IOException { } private static void doCopyFile ( File srcFile , File destFile , boolean preserveFileDate ) throws IOException { } public static void copyDirectoryToDirectory ( File srcDir , File destDir ) throws IOException { } public static void copyDirectory ( File srcDir , File destDir ) throws IOException { } public static void copyDirectory ( File srcDir , File destDir , boolean preserveFileDate ) throws IOException { } public static void copyDirectory ( File srcDir , File destDir , FileFilter filter ) throws IOException { } public static void copyDirectory ( File srcDir , File destDir , FileFilter filter , boolean preserveFileDate ) throws IOException { } private static void doCopyDirectory ( File srcDir , File destDir , FileFilter filter , boolean preserveFileDate , List < String > exclusionList ) throws IOException { } public static void copyURLToFile ( URL source , File destination ) throws IOException { } public static void copyURLToFile ( URL source , File destination , int connectionTimeout , int readTimeout ) throws IOException { }

Fix:
throw new IllegalArgumentException ( ( "Parameter<seq2seq4repair_space>'directory'<seq2seq4repair_space>is<seq2seq4repair_space>not<seq2seq4repair_space>a<seq2seq4repair_space>directory:<seq2seq4repair_space>" + directory ) ) ;